Inherently “conductive polymers” (π-conjugated conductive polymers) and non-conductive polymers with conductive dopants are useful as biocompatible polymeric coating materials for preexisting electrodes, probes, and sensors providing unique electrical, biochemical and electroactive properties. The monomers that polymerize to form conductive polymers can comprise one or more of 3,4-ethylenedioxythiophene (EDOT), pyrrole, anilines, acetylenes, thiophenes, and blends thereof.
Surface and bulk materials currently used as electrodes for biomedical devices offer limited biocompatibility, resulting in tissue injury and inflammation in the vicinity of the implanted device. In addition to limited biocompatibility, stimulation of chronic negative immune system reactions often lead to biofouling of existing implants of electrodes and erosion of device surface materials. Various biological tissues, including the central nervous system (CNS) react negatively to implanted devices, varying in severity according to the site of implantation, the materials used and differences in electrode geometries and implantation methodologies. Chronic rejection of the implantable devices in the CNS can be characterized by a hypertrophic reaction from surrounding astrocytes with increased expression of filament proteins and vimentin. In addition to protein adsorption to the device surface, microglial cells and foreign body giant cells envelop the implanted devices resulting in encapsulation of the device and formation of high electrical impedance fibrous scar tissue. This diminishes, and eventually negates signal transduction between the tissue and the device. Similar foreign-body responses are found throughout human and animal tissues including major targets for novel implanted biomedical devices including the brain, heart, and skin. Bioincompatibility represents a key weakness of new implantable biomedical devices currently being developed and is the foremost roadblock to successful in vivo testing and usage.
Surface modification of implantable electrodes and sensors should provide improvements in both their long term biocompatibility and eletro-functionality. It would be highly desirable to design electrode devices which could intimately interface electrode sites to living tissue, as well as to facilitate efficient charge transport from ionically conductive tissue to the electronically conductive electrode and induce surrounding tissue to attach or interface directly to the implanted device.